03 Seadoo GTX S/C Issues

Hello folks.....
Looking for some help with my ski. Has 75.3 hours on it, always maintained, oil change every season, etc. Moved from sea level last year to northern new mexico. Put the ski out on the water, wouldn't get up to full rpm. Max has been 5500. Max speed is 38mph. Took to the local dealer and they gave it a tune up....now we have full rpm...7800, but never more than 42mph. Dealer said my prop was incorrect for altitude, so I swapped stock prop with a solas 17/23. Also replaced stock wear ring with stainless steel ring while apart. Got a deal on a Work Racing Maxiloader grate, so that was installed also.

First test on the lake was day before yesterday. Max speed is back to 38mph, and max rpm is 5700. Dealer here offers no help or solutions, so I turn to you guys. Our mechanic at the shop swears it is the s/c, but I'm unsure....truck mechanic not a ski mechanic. Any info or direction will help. Thanks folks

I did some looking around online real quick....
Any feedback on an 11/18? or still too much?
Decided we are going to rebuild the head...found some metal shavings when we pulled the valve cover. When we pull it all apart going to shave the head a few thousandths, install a few other performance parts.
Any suggestions or feedback?